Wisconsin

Sport fish are thriving but invasive species threaten Green Bay, new report says

Tom Kemos of Oconomowoc holds a walleye caught and released while fishing in Green Bay last summer. A report released Thursday says walleye remains a trophy fishery in the bay, spotted muskies have benefited from stocking and lake sturgeon are recovering.

Walleye and other sport fish populations are doing well in Green Bay, but the vast body of water that is a part of Lake Michigan continues to be ravaged by invasive species and a cocktail of nutrients that have created a dead zone bereft of oxygen.

These are some of the conclusions by researchers at the University of Wisconsin Sea Grant Institute and University of Wisconsin-Green Bay in a report Thursday on the health of the bay.

The study is the third "state of the bay" report. The two previous studies were in 1990 and 1993. In the past 20 years, the report reveals, a mixed bag of factors has affected the waters.

"It's in constant change," said H.J. "Bud" Harris, a professor emeritus of natural and applied science at UW-Green Bay and one of the authors. "The bay is extremely dynamic."

The authors gathered water quality data and other information from a host of sources and found, among other things, that walleye populations are unchanged and remain a trophy fishery, spotted muskies have benefited from stocking and lake sturgeon are recovering.

Since 2000, the number of boat licenses in the region has risen or remained about the same, depending on the county abutting the bay. The same is true with fishing license sales.

Also, ammonia levels have declined. That's primarily due to upgrades in wastewater treatment by the Green Bay Metropolitan Sewerage District.

Beach closings have been declining in recent years because of improved monitoring programs and efforts to control sources of bacteria near the beaches.

Water quality levels likely hit their low point in the 1970s before the Clean Water Act began to mandate limits on pollutants that could be discharged into water bodies by such sources as factories and wastewater treatment plants.

But levels of toxic chemicals, such as polychlorinated biphenyls, remain at unacceptable levels. The massive cleanup projects on the Fox River should begin to produce positive results in the coming years, the study found.

The emergence of new invasive species also has taken a toll on the bay. Zebra mussels arrived in 1991. More recent arrivals have beenEurasian ruffe in 2002; quagga mussel in 2003; and the bloody red shrimp in 2007.

'Gunk in the water'

For now, phosphorus and nitrate concentrations are rising. Both can come from various sources, but agriculture is a key contributor. Another pollutant, known as total suspended solids, which the scientists in their report termed "gunk in the water," also is rising.

Suspended solids are the algae, soil and decaying plant matter that remain suspended in the water. They cut visibility and can harm aquatic life. About 25 dump truck loads of sediments are released into the bay every day, according to the study.

Water clarity in Green Bay averages half a yard. It should be twice that to meet targets for a healthy ecosystem, the study says.

The data on phosphorus — one of the most important chemicals influencing Green Bay — shows that it rises and falls over time. But it has risen since 2009, and the accumulation in the bay has helped create a dead zone with little or no aquatic life. It's a situation similar to those in Lake Erie and the Gulf of Mexico.

Researchers revealed its presence last summer and said it may cover as much as 40% of the bay, beginning about 8 miles northeast of the city of Green Bay.

Harris said Green Bay and the Fox River had dead zones in the 1970s. With better pollution controls and a ban on phosphorus in detergents, conditions turned around. But phosphorus levels are trending up again, water quality data shows.

Phosphorus spurs algae blooms, which die and decay and the bacteria they produce gobbles up oxygen from the water.

Harris said it takes about a year for water in the bay to leave and enter Lake Michigan.

"What that means is that if you shut down the sources (of pollution), you ought to see a relatively rapid recovery of these nutrient sediments," he said.